The techniques of rapid reaction kinetics will be employed to study the mechanisms of ligand binding to subunit proteins in which there are cooperative interactions between subunits. Specifically, the aim is to elucidate the mechanism of oxygen binding to hemoglobin, the mechanism of self-assembly in Tobacco Mosaic Virus, and the mechanism of cooperative interactions in aspartate transcarbamylase. The results of these investigations of the functional properties of the three proteins will be interpreted in terms of their detailed structural properties now being determined by x-ray crystallography.